HTML writer: ensure that line numbers in code blocks get id-prefix.

Closes #5650.

src/Text/Pandoc/Writers/HTML.hs

@@ -776,8 +776,8 @@ blockToHtml opts (CodeBlock (id',classes,keyvals) rawCode) = do
              then do
                modify $ \st -> st{ stCodeBlockNum = stCodeBlockNum st + 1 }
                codeblocknum <- gets stCodeBlockNum
-               return ("cb" ++ show codeblocknum)
-             else return id'
+               return (writerIdentifierPrefix opts ++ "cb" ++ show codeblocknum)
+             else return (writerIdentifierPrefix opts ++ id')
   let tolhs = isEnabled Ext_literate_haskell opts &&
                 any (\c -> map toLower c == "haskell") classes &&
                 any (\c -> map toLower c == "literate") classes
@@ -800,7 +800,9 @@ blockToHtml opts (CodeBlock (id',classes,keyvals) rawCode) = do
            addAttrs opts (id',classes,keyvals)
              $ H.pre $ H.code $ toHtml adjCode
          Right h -> modify (\st -> st{ stHighlighting = True }) >>
-                    addAttrs opts (id'',[],keyvals) h
+                    -- we set writerIdentifierPrefix to "" since id'' already
+                    -- includes it:
+                    addAttrs opts{writerIdentifierPrefix = ""} (id'',[],keyvals) h
 blockToHtml opts (BlockQuote blocks) = do
   -- in S5, treat list in blockquote specially
   -- if default is incremental, make it nonincremental;

test/command/5650.md

@@ -0,0 +1,22 @@
+````
+% pandoc --id-prefix foo
+```haskell
+a
+b
+```
+^D
+<div class="sourceCode" id="foocb1"><pre class="sourceCode haskell"><code class="sourceCode haskell"><span id="foocb1-1"><a href="#foocb1-1"></a>a</span>
+<span id="foocb1-2"><a href="#foocb1-2"></a>b</span></code></pre></div>
+````
+
+````
+% pandoc --id-prefix foo
+``` {.haskell #bar}
+a
+b
+```
+^D
+<div class="sourceCode" id="foobar"><pre class="sourceCode haskell"><code class="sourceCode haskell"><span id="foobar-1"><a href="#foobar-1"></a>a</span>
+<span id="foobar-2"><a href="#foobar-2"></a>b</span></code></pre></div>
+````
+